Modulating pressure relief valves are frequently provided in fluid systems to control the rate of pressure rise in an actuator, such as a fluid operated clutch. It is desirable to have modulating pressure relief valves that are compact and easy to manufacture. In most conventional applications, the modulating relief valve includes a separate spool and a load piston each arranged in axially separated positions to each other in one bore. Naturally, this increases the physical size of the valve arrangement.
Other valve arrangements are known that provide compactness by having multiple valve members concentrically nested in a single bore. One of these valve arrangements provides multiple function by having three valving elements concentrically disposed one within the other. However, in this arrangement, two of the valving elements function in a flow controlling relation with the housing and only one of the valving elements functions in a flow controlling relation with one of the other valving elements. This does not allow the control of one function with respect to the control of another function.
Another of these valve arrangements provides multiple function by having several valving elements concentrically arranged in a single bore. However, this arrangement requires an external electrical signal to energize a solenoid that in turn moves one of the valving elements to initiate valve operation. Furthermore, this arrangement requires a special multipiece valving element that must cooperate with the solenoid valving element and a separate valving element. The special multipiece valving adds complexity to the valve arrangement but is required in order to maintain the compactness.
The present invention is directed to overcoming one or more of the problems as set forth above.